Biochemical Changes in Aquatic Organisms in a Warming World

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Our world is warming up yet we do not fully understand the ramifications of this far-reaching, globally-significant, event. Plants and animals respond to increasing water temperature by adjusting the chemical composition of their cell membranes through the process known as homeoviscous adaptation. This biochemical adaptation involves increasing the amount of saturated fatty acids at the expense of polyunsaturated fatty acids (PUFA). The loss of PUFA as water heats up, particularly the loss of omega-3 long-chain PUFA (LC-PUFA; i.e. 20- and 22-carbons long), has enormous implications for all life. Phytoplankton contribute >½ of the total primary production globally and are the main producers of omega-3 LC-PUFA. However, we do not yet understand how climate warming will affect the production (source) and distribution (fate) of these essential compounds. Climate modelers predict an increase in surface air temperatures and in the number of extreme heat days; with concomitant increases in surface water temperatures (especially in shallow productive systems). These temperature increases are expected to be most profoundly felt in temperate and northern regions. The large (> 1 million) number of small wetlands (with high connectivity to terrestrial ecosystems) in these regions (where water temperatures were colder and EFA production was high) suggest that it is in these regions of the biosphere that freshwater-derived LC-PUFA are being produced in the greatest quantities. A large body of evidence demonstrates that omega-3 LC-PUFA are critical for the health and well-being of animals, supporting enhanced growth rates and reproductive capacities and contributing in demonstratively-positive ways to cardiovascular, immunologic, and cognitive health. Animals could simply synthesize LC-PUFA from shorter-chain (i.e. 18-carbon) fatty acid precursors, however, studies with a variety of fishes and mammals (including humans) have demonstrated that the conversion of 18-carbon omega-3 FA to LC-PUFA such as EPA (20:5n-3) and DHA (22:6n-3) is “unreliable and restricted” and that therefore the majority of the essential fatty acids (EFA) found in the vertebrate brain, nervous tissue, cardiovascular system, retina, sperm and milk come from the diet. Omega-3 LC-PUFA like EPA and DHA are not produced by terrestrial plants or insects. Thus, terrestrial organisms ultimately obtain much of their omega-3 LC-PUFA from aquatic organisms (e.g. insect emergence; fish) which, in turn, obtain them from algae. This “pre-formed” source of EFA is the most efficient way for terrestrial (and aquatic) animals to obtain these essential biochemicals in amounts sufficient to maintain them in optimal condition. Using lab and field studies, my students (1 PDF, 2 PhD and 1 MSc) and I, and my colleagues, will address critical knowledge gaps thereby transforming our understanding of how climate warming affects the production and re-distribution of aquatic-derived omega-3 LC-PUFA. We will: 1) quantify, under controlled laboratory conditions, the production of PUFA in biochemically-relevant lipid classes (e.g. phospholipids, diacylglycerols) as a function of water in several cosmopolitan algal species from several representative taxa, and 2) gently warm portions of natural ponds and measure both the internal production of PUFA in algae and their trophic transfer to zooplankton and the larval stages of insects and also the flux of LC-PUFA (redistribution) from the ponds onto adjacent terrestrial systems (via insect emergence). This new conceptualization of how climate change affects LC-PUFA production will fundamentally transform our appreciation of the key role that our aquatic resources play and how this role may be altered in a warming world.